The invention relates to methods and apparatus for inducing physical changes in metal objects in general and making use of pulsed magnetic force (PMF) energy therefor, in particular.
The employment of PMF, for forming, joining or welding of metal objects is known in the art. In this process, current is rapidly discharged through a coil, which is proximal to the workpiece. Owing to eddy currents in the workpiece, an intense magnetic pressure builds up, which may perform work on at least a portion of the workpiece. Typically, the portion of the workpiece, which is proximal to the working coil of the PMF apparatus, is induced into a rapid movement and the kinetic energy associated with this movement gives rise to said physical change. The change may be forming namely a change in the shape of the object. At times, the rapid movement of said portion is induced only on a microscopic scale. For example, in the case of joining or welding two metal workpieces, portions thereof are placed into close proximity and they in fact touch one another. But nevertheless notwithstanding this close proximity some clearance between the two remains even if only on a microscopic scale which permits a short rapid movement of a portion of at least one of the workpieces (obviously over only a very short distance). This suffices for the build-up of kinetic energy, which dissipates upon impact with a portion of the other workpiece and may give rise to joining or welding of the two workpieces to one another.
The present invention is directed to a method and apparatus for working, i.e. inducing physical change in at least one metal workpiece. The term xe2x80x9cphysical changexe2x80x9d denotes structural change in form or shape, cutting off of a portion of a workpiece, perforation of a workpiece, joining of two or more workpieces to one another or welding two workpieces or portions thereof to one another. The term xe2x80x9cjoiningxe2x80x9d used before and further below means to denote a tight engagement of two workpieces to one another, for example, tight fitting of a generally cylindrical object over a tubular object fitted within it; and the term xe2x80x9cweldingxe2x80x9d, in distinction from joining, means to denote a very tight interaction of the surfaces of two objects, e.g. metalurgical bonding of at least a portion of the two workpieces.
The method and apparatus of the invention make use of pulsed magnetic force (PMF) energy. In accordance with the invention, PMF energy is combined with another energy from a separate energy source which acts synergistically with the PMF energy to impart a physical change. The other energy source (to be referred to herein at times as the xe2x80x9cauxiliary energy sourcexe2x80x9d) may be another PMF energy, may be a mechanical energy source, and many others.
In accordance with a first aspect of the invention there is thus provided a method for inducing a physical change in at least one metal workpiece, comprising:
(a) transferring at least one pulse magnetic force (PMF) energy to at least a portion of the at least one workpiece for inducing an intense magnetic pressure therein; and
(b) transferring an auxiliary energy at least partially co-extensive with the PMF energy to the at least a portion of the workpiece whereupon the PMF and auxiliary energies combine to yield the physical change.
In accordance with another aspect of the invention there is provided an apparatus for inducing a physical change in at least one metal workpiece, comprising:
(i) at least one PMF unit with a forming coil for the discharge of current therethrough to induce an intense magnetic pressure in at least a portion of the metal workpiece; and
(ii) at least one auxiliary energy source for transferring, at least partially co-extensive with the current discharge through the forming coil, an auxiliary energy to the at least a portion of the workpiece such that said pressure and auxiliary energy synergize to yield said physical change.
The term xe2x80x9ctransferring energyxe2x80x9d or any similar term which may be used herein, means to denote the transfer of energy to a workpiece in a form which at least partially acts to yield said physical change. The term xe2x80x9cmetal workpiecexe2x80x9d refers to any metal object which is to be worked by the method or apparatus of the invention, which may be a cylindrical object which is to be joined or welded to a tubular or another cylindrical objection; a metal plate which is to be formed, cut or perforated; etc. As will be appreciated, the invention is not limited to a workpiece of any specific kind but rather can be applied for a myriad of different workpieces and for inducing a wide variety of different physical changes.
The term xe2x80x9ccombination of energiesxe2x80x9d or the like means to denote the timed activation of the at least two energy sources to transfer their respective energies to the at least one workpiece such that the periods of their transfer at least partially overlap, whereby the combined effect of the two energies, as far as inducing the physical change, is substantially larger than the physical change which may be imparted by only one of the energy sources. The combination of energies in accordance with the invention gives rise to a variety of improvements over the use of PMF alone. For example, in the case of welding or joining of two metal workpieces to one another, the same result may be achieved with a lower PMF energy as compared to PMF alone. This may have design consequences as the generation of a large PMF necessitates large capacitor banks and thus an apparatus in accordance with the invention may have an overall smaller size.
Additionally, the present invention allows the achievements of results, which may be difficult to achieve in accordance with the prior art. For example, in the case of welding two tubular workpieces to one another, with one enveloping the other, the strong impact of the external one onto the internal one, may give rise to squeezing or crushing of the internal tubular workpiece. However, in accordance with the invention, which permits use of smaller PMF pulses for achieving the same effect, such an undesired effect may be eliminated or reduced. In the case of welding, the combination of energies in accordance with the invention may give rise to an increase of the area of the weld.
At least for the case of welding, it is preferred that the time period overlap be substantial, meaning that at least one of the energies is applied such that throughout most of its period of application, it overlaps the other applied energy. This may mean, for example, that both may begin and end simultaneously, both may begin simultaneously and end in succession, both may begin in succession but end simultaneously, one beginning and ending during the period the other energy is applied, and various combinations of these scenarios.
While one energy source is always a PMF energy source from a PMF device, to be referred to herein at times as xe2x80x9cprimary PMF energy sourcexe2x80x9d/xe2x80x9cprimary PMF devicexe2x80x9d, the other energy source may be selected from a wide variety of different sources. In accordance with one preferred embodiment, the other energy source is an auxiliary PMF energy source of a different specification. In accordance with other embodiments, the other energy source is a device for generating a mechanical shock wave or mechanical vibrations in the workpiece; a device which can generate ultrasonic vibrations within the object, e.g. a device as customary used in ultrasonic welding; a device for transferring an electric current through an interface between portions of workpieces which are to be welded to one another, such as that used in resistant welding; etc.
It should be noted that the term xe2x80x9cprimaryxe2x80x9d used above and further below, does not mean to denote that this energy source is of prime importance as compared to other sources of energy used in accordance with the invention. Similarly, the term xe2x80x9cauxiliaryxe2x80x9d should not be understood as meaning secondary in importance. Rather, these terms are used merely for the sake of convenience. It should be appreciated that in order to yield any efficient physical change in accordance with the invention is achieved by the combination of the primary and the auxiliary energy sources, as mentioned above and further below.
The primary and the auxiliary energies which are used in combination in accordance with the invention, are superimposed, namely they are generated such that there are applied for periods of time overlapping one another over substantial portions thereof. In accordance with one embodiment, the primary PMF energy is generated simultaneously with the auxiliary energy. In accordance with another embodiment, the auxiliary energy is initiated prior or after the primary PMF energy.
At times, the total amount of the transferred primary energy may be larger than the total amount of the transferred auxiliary energy, at times they may be about the same or at time the total of the auxiliary energy may exceed the total of the primary energy.
In accordance with one embodiment, the auxiliary energy is PMF energy. The apparatus in accordance with this embodiment comprises two discharge circuitries, one for discharging a primary electric current through the primary working coil, and another for discharging an auxiliary electric current through an auxiliary working coil, which may be the same or different than the primary working coil. The auxiliary electric current has a frequency which is substantially different (larger or smaller) than that of the primary electric current, typically larger, e.g. 5-100 times larger. For example, the primary pulse may have a period of 100-200 sec (a frequency of 10,000-5,000 Hz, respectively) while the period of the auxiliary pulse may have a period of about 6-10 sec. The auxiliary pulse in such a case is typically initiated after a certain period of time from the initiation of the primary pulse, e.g. after about 20-40 sec, respectively (when the primary pulse is close to its pick). The auxiliary pulse is timed so as to synergize with the primary pulse to yield said physical effect.
The amplitude of the primary current may be larger than the primary current, e.g. 2-50 times that of the primary current, or at times may be about the same.
By another embodiment, said auxiliary energy is a mechanical energy imparted by inducing rapid movement in at least one of the two metal objects. Such movement may be a mechanical shock or vibrations. In accordance with one embodiment, the mechanical energy is imparted onto the at least one metal object by means of a mechanical waveguide. The waveguide may be associated with an auxiliary working coil connected to a current discharge circuitry which, by means of a PMF, generates mechanical vibration waves in said waveguide which are then transmitted to the metal object. Alternatively, the waveguide may be associated with a discharge-in-fluid (DIF) device, which generates a shock wave, which is then transmitted by the waveguide to at least one of the objects. The DIF device comprises a fluid chamber with discharge electrodes provided within the chamber for discharging an electric current between them and through the fluid. When an electric current is discharged between the electrodes, a plasma forms within the fluid which generates a shock wave within the fluid which is then transmitted to the waveguide. The fluid is typically an aqueous solution.
In accordance with another embodiment, the mechanical energy is an ultrasonic energy.
While the present invention is applicable in general for yielding a more efficient physical change of at least one workpiece, it is particularly applicable to welding of two metal workpieces to one another (xe2x80x9cthe welding embodimentxe2x80x9d). The welding embodiment is a preferred embodiment of the present invention. In accordance with this preferred, welding embodiment, there is provided a method for welding two metal objects to one another, comprising:
(a) during a first period of time, generating a primary pulsed magnetic force (PMF) energy by discharging a primary electric current through a primary working coil so as to induce an intense magnetic pressure on at least one portion of a first of the two metal objects to cause said portion to move towards an impact at least one other portion of the second metal workpiece;
(b) during a second period of time, transferring to at least one of the two metal objects, an auxiliary energy which is other than said primary PMF energy, said first time period and said second time period overlap one another over at least a substantial portion of one of said first or said second time periods, whereby said auxiliary energy in combination with the PMF energy causes welding of the at least two portions to one another.
In accordance with the welding embodiment there is further provided an apparatus for welding of two metal objects to one another comprising:
a primary electric discharge circuitry with a primary working coil for generating, during a first period of time of a working cycle of the apparatus, a pulsed magnetic force (PMF) to cause at least a portion of a first of the two metal objects to move towards an impact of this said portion of a second of the two metal objects; and
a device for generating, during a second period of time of the working cycle of the apparatus, an auxiliary energy and transferring it to at least one of the two metal objects which said first period of time and said second period of time overlap one another over at least a substantial portion of one of said first or said second period of time, whereby said auxiliary energy in combination with the primary PMF energy, causes welding of the two portions to one another.
For welding, a combination of PMF energy with any of the energies discussed above may be applicable. In addition, in the case of welding, the auxiliary energy may also be an electric current induced to pass through the interface between portions of the two metal workpieces, which are to be welded to one another. This embodiment may make use of electrodes of the kind customarily used in resistant welding, which are generally known per se.
The auxiliary energy, in accordance with another embodiment, particularly applicable to the case of welding, but may also be applicable to other embodiments dealing with different kinds of physical changes, mentioned above, is an auxiliary energy source which causes heating of the at least a portion of the metal workpiece. Such heating may be achieved by an ultrasound energy source, generally known per se, may be achieved by induction heating which is also generally known per se, and by a variety of other heating means known per se. In this case, after the workpiece has been heated, the effect of the PMF may be more pronounced than without heating.
As may be appreciated, the auxiliary energy source used in the method and apparatus of the invention may be a combination of the auxiliary energy sources discussed above. Thus, in such a case the energy applied to the metal workpiece is a combination of three or more superimposed energies. For example, a combination of induction heating and an auxiliary PMF.